Method of bonding porcelain to gold castings and articles resulting therefrom



lee Patented Nov. 18, .1958

METHOD OF BUNDlNG PORCELAIN T GOLD CAglpflINGS AND ARTICLES RESULTING THERE- FR Gerald J. Axelrod and Herman Axelrod, Philadelphia, Ya.

No Drawing. Application May 15, 1956 Serial No. 584,882

9 Claims. (Cl. 117-70) This invention relates to a method of bonding porcelain to castings of gold or gold alloys, the porcelain used in the method and the article resulting from the method.

T-he invention, while of general application, is particularly adapted for use in fabricating porcelain-gold dental prosthetics, such as crowns and bridges.

It is an accepted fact that porcelain is superior to plastics withregard to transparency and color shadings and with regard to behavior in the mouth. Yet plastics are being employed in dental restorations instead of porcelain. This is so because porcelain cannot be successfully bonded directly to gold castings by heat.

We have discovered what we believe to be one of the basic causes for this failure and that is the difference between the coefiicient of expansion and contraction of the gold and that of the porcelain. Depending upon which coefiicient is larger, heating and subsequent cooling of contacting layers of gold and porcelain will place one of the layers under compression and the other under tension with the result that either no bond will form at all, or if it does form it will be weak and temporary and a check will quickly develop in the porcelain.

We have discovered that the incorporation of powdered gold or gold alloy in the porcelain will narrow the difference between the coefficient of expansion and contraction of the porcelain and that of the gold so that a firm bond can be effected between them with heat and without an intermediate cementitious layer.

We have further discovered that if the gold or gold alloy in the porcelain and that in the casting is substantially free of impurities which are oxidizable in air at or below approximately 1850 F., the bond between the casting and the porcelain is strengthened and undesirable opacity in the porcelain is minimized.

The method of casting the gold or gold alloy into a prosthetic or other form is not within the purview of the invention. While pure gold may be employed for the casting, gold alloyed with such hardening metals as silver, palladium and platinum is preferred. The fusion point of the gold or gold alloy should be between 1925 and 1970 F. Such non-oxidizable gold alloys are available commercially.

Thel porcelain which is utilizable in the invention is standard dental porcelain having a fusing point below that of the gold or gold alloy in the casting and, if the casting is a dental bridge, below that of the solder used in the bridge. The preferred fusion point of the standard dental porcelain is approximately 1850 F.

The powdered gold or gold alloy which is mixed dry with the porcelain in certain proportions as will appear hereinafter should be of the same composition as that of the casting. It may however be different provided it is of the non-oxidizing type and has a fusion point above that of the porcelain.

While the invention may be applied to any gold or gold alloy casting, it has particular advantages and meets a particular need in the art of dental prosthesis. Hence, the details of the invention will be set forth hereinafter layer, or approximately .025% by volume.

as it is applied to casting of dental'crowns andbridges. The invention is carried out as follows:

1) The crown or bridge casting of gold, silver and palladium with a minute amount of platinum. and having a fusion point between 1925 and 1970 F. .is cleaned with a solution of HCl to remove surface oxides, if any.

(2) A dry mixture is made of standard dental porcelain having a fusion point of approximately l850 F. and powdered, 250 mesh, gold alloy of the same type as used in the casting. The mixture contains approximately 0.1% by volume of the powdered gold alloy.

(3) The required amount of the porcelain-gold mix is combined with water and/ or diluted glycerine to make a brushable paste which is applied to the casting, dried and then inserted in an oven for baking at approximately 1750 F. for about 20 minutes. A rough or fritted biscuit-bake results.

(4) An additional or build-up layer of porcelain-gold mix is brushed or applied on the biscuit bake except that this layer contains half the amount of gold alloy as that in the first layer or approximately 0.05% by volume. The casting with the build-up layer is subjected to the same drying and baking procedure as Was used in the biscuit bake.

(5) A final or finishing layer of porcelain-gold mix is applied over the build-up layer except that the finishing layer contains half the gold alloy content of the build-up The casting with the finishing layer is dried and then baked in the oven for approximately 20 minutes at the porcelain fusion temperature of about 1850" F. to yield the smooth finish required of an incisal layer.

The biscuit bake or first layer of porcelain-gold mix contains the greatest quantity of gold in order that the coefficient of expansion and contraction of this first layer should more closely approximate the coefficient of the casting itself. The gold content of subsequent build-up and finishing layers decreases to provide a gradient of the coefficient of expansion and contraction of the layers. This not only creates a strong bond between the first layer and the casting but also between the porcelain layers themselves. At the same time a gradient reduction of the gold content to the point where there is only a small quantity in the finishing layer provides the type of transparency in the porcelain which has not been attained heretofore in prosthetics using porcelain facings.

Moreover, the use in the casting and in the porcelain of gold or gold alloys substantially free of components which can oxidize at or below the fusion point of the porcelain contributes to strengthening the porcelain to gold bond and to the superior type of transparency attainable in the porcelain.

We claim:

l. A ceramic adapted to be bonded by heat upon gold or gold alloys comprising porcelain admixed with a metal selected from the class consisting of gold and gold alloys which are substantially free of impurities oxidizable in air at or below approximately 1850 F., said metal being 250 mesh and present in 0.025 to 0.1% by volume.

2. A process of bonding porcelain to a casting of gold or gold alloys comprising applying successive layers of porcelain containing powdered gold or gold alloys upon the casting and separately baking each layer on the preceding one before the next layer is applied, the metal content of the porcelain progressively decreasing from the innermost to the outermost layer, the metal content of the innermost layer being approximately 0.1% by volume.

3. A process of bonding porcelain to a casting of gold or gold alloys comprising applying to the casting a layer of porcelain having a fusing point below that of the casting in which powdered 250 mesh gold or gold alloy is dispersed in approximately 0.1% by volume, baking the casting at approximately 1750 F. to yield a biscuit bake, applying a second layer of porcelain-gold mixture in the biscuit bake, the gold content of said second layer being less than the first layer, again baking the casting at approximately 1750 F., applying a third or finishing layer of porcelain-gold mixture on the second layer, the gold content of the finishing layer being less than that of the second layer and finally baking the casting at approximately 1850 F.

4. The process of claim 3 wherein the gold content of the second porcelain layer is half of the first and that of the third layer is half of the second.

5. The process of claim 3 wherein said gold alloy is substantially free of impurities which are oxidizable in air at or below approximately 1850 F.

6. A casting fabricated of gold upon which is heat bonded superimposed layers of porcelain containing powdered gold dispersed therein, the innermost layer containing approximately 0.1% gold by volume, the overall gold content of all the layers being approximately 0.058% by volume.

7. A casting fabricated of gold upon which is heat bonded superimposed layers of porcelain through which powdered 250 mesh gold has been dispersed, the innermost layer containing approximately 0.1% gold by volume, the overall gold content of all the layers being approximately 0.058% by volume.

8. A casting fabricated of a metal selected from the class consisting of gold and gold alloys substantially free of impurities oxidizable in air at or below approximately 1850 F. upon which is heat bonded successive superimposed layers of porcelain through which said metal in 250 mesh particle size has been dispersed, the metallic content of the porcelain decreasing progressively from the innermost to the outermost layer with the innermost layer having' a metallic content of approximately 0.1% by volume.

9. The casting of claim 8 wherein there are three superimposed porcelain layers, each successive layer containing approximately half of the metal content of the layer below.

References Cited in the file of this patent UNITED STATES PATENTS 30,684 Mofiitt Nov. 20, 1860 2,697,670 Gaudenzi et a1 Dec. 21, 1954 FOREIGN PATENTS '1 120,845 Australia Ian. 10, 1946 656,503 Great Britain Aug. 21, 1951 OTHER REFERENCES Pearson: The Production of Special Glasses, The Industrial Chemist and Chemical Manufacturer, volume 18, February 1942, pp. 60-63.

Hackhs Chemical Dictionary, third ed. (1944), p. 665. 

2. A PROCESS OF BONDING PORCELAIN TO A CASTING OF GOLD OR GOLD ALLOYS COMPRISING APPLYING SUCCESSIVE LAYERS OF PORCELAIN CONTAINING POWDERED GOLD OR GOLD ALLOYS UPON THE CASTING AND SEPARATELY BAKING EACH LAYER ON THE PRECEDING ONE BEFORE THE NEXT LAYER IS APPLIED, THE METAL CONTENT OF THE PORCELAIN PROGRESSIVELY DECREASING FROM THE INNERMOST TO THE OUTERMOST LAYER, THE METAL CONTENT OF THE INNERMOST LAYER BEING APPROXIMATELY 0.1% BY VOLUME. 